The invention relates to a process for the contour correction of the luminance signal in a television camera in which a horizontal contour signal is added to a relatively poorly defined luminance signal in order to increase the vertical resolution, and a vertical contour signal is added thereto in order to increase the horizontal resolution.
The function of contour signals of this type can be explained most instructively by considering horizontal and vertical lines which are recorded and are to be transmitted by the television camera. Here "horizontal" signifies the direction of a line of the electronic scanning. With these lines, very great demands are placed on the electronic scanning and on the transmission in respect of the resolution of the picture source and the signal transmitted for the reproduction of a sharply defined picture. The finite expansion of the picture points scanned by the electron beam impose limits on the resolution. This can be seen most clearly in that horizontal and vertical sharp lines of the picture source in the case where the luminance information changes abruptly at right angles to the line direction, appear to be poorly defined in the picture reproduction.
To the luminance signal obtained from the modulated electron beam can be added a vertical contour signal (in the following referred to as W.sub.V) in order to improve the definition of horizontal lines, and a horizontal contour signal (in the following referred to as W.sub.H) in order to improve the definition of vertical lines. This constitutes a simple addition of a signal which weakens the edges of the lines and strengthens the center. The horizontal contour signal W.sub.H (equal to line frequency) here consists in a signal which repeats itself line-by-line and which in the edge regions of the image point, located in the scanned line, of a vertical, for example white line, deducts luminance electrically from the relatively poorly defined luminance signal and in the region of the center of the image point adds luminance. This also correspondingly applies to the vertical contour signal W.sub.V (equal to picture frequency). It is thus ensured that the relatively poorly defined luminance signal which would reproduce clearly defined horizontal and vertical lines in a relatively poorly defined fashion, becomes a clearly defined luminance signal which also reproduces the horizontal and vertical clearly defined lines equally clearly.
However, real picture sources do not consist merely of horizontal and vertical lines. For example, there are intersection points of such horizontal and vertical lines. In the region of these intersection points, the known process of adding a vertical and horizontal contour signal gives rise to unpleasant effects. The addition of luminance information in the center of white lines gives rise to too great an emphasis on luminance at the intersection point of the line centers, since both the horizontal and the vertical contour signal add luminance. On the other hand, for example, in the edge regions of a vertical line which are located at the intersection point on the center of the intersecting horizontal line, the horizontal contour signal W.sub.H serves to withdraw luminance information so that these two zones which actually lie in the center of the horizontal line, which is clearly defined on account of the vertical contour signal W.sub.V, again become poorly defined. This also correspondingly applies to the two edge zones of the horizontal line which come to lie in the central region of an intersecting vertical line. The double correcting action of the horizontal and vertical correcting signals W.sub.H and W.sub.V thus gives rise to breaks in the intersecting horizontal and vertical lines in the region of an intersection point. This is referred to as a so-called correlation error.
An intersection point is here reproduced by an over-defined intersection of the line centers and by a surrounding poorly defined halo.